The present invention relates to data recorders and, more particularly, to those data recorders employing cyclic recording and readback operations which may include a portion of a cycle during which no signals are sensed.
As many new products reach the marketplace in the digital signal recording area, there is a continuing desire to increase the areal recording density. While in many instances the record media can retain such increased densities, the data recorders have to be substantially changed. In many instances, there is no forward/backward compatibility between the original low density recording and the new high density recording. Such incompatibilities, while in many instances are unavoidable, add to the cost of signal recording and are to be avoided if at all possible.
Forward/backward compatibility was achieved in one-half inch tape digital data signal records originally when one-half inch tapes used NRZI recording at 200, 556 and 800 bytes per lineal inch. Operator selection was required for the digital data recorders to operate with different density tapes. When phase encoded recording came into being, all phase encoded tapes were identified by a burst of phase encoded signals in a plurality of tracks at the beginning of tape. Such identification was called a TEID. Such tapes were used in conjunction with NRZI tapes, which still required operator intervention for successful recorder operation at multiple lineal densities. The increase of areal densities can also be achieved by increasing track density while not changing lineal density, or by simultaneously changing both densities.
Higher density signal recording often yields an effective higher data rate. This is particularly true with increased lineal densities. When increasing areal densities without increasing the lineal density, the burst data rate does not increase nor does the effective (average) data rate increase. Accordingly, it is desirable to increase track density while simultaneously increasing the effective data rate, all at a minimal cost in the recorder.
As mentioned above, multiple densities in one-half inch tapes required manual selections. With present day automation, it is highly desirable to increase the flexibility of recorders for enabling automatic recorder operation than is amenable to diverse track densities and diverse lineal densities. Many recording devices transfer data signals only a portion of the time; such as rotating head recorders, reciprocating head recorders, during track switching in any recorder, and those recorders employing so-called sector servos. The time remaining in recorder cycles is termed "dead time"--no data is transferred. Such dead time is dedicated for servoing, moving the magnetic medium with respect to a transducer, or vice versa, as well as performing other miscellaneous control functions. It is desirable to minimize the adverse effect on data rates of such dead time in signal recorders. When employing such automatic means, the arrangement on the record media should facilitate the automation of multiple density recording for achieving fully automatic forward/backward compatibility among diverse record members.